The present invention relates generally to the production of fuel gas by the gasification of coal and the desulfurization of the fuel gas prior to the use thereof in a power utilization device. More particularly, the Present invention relates to production of fuel gas in a two-stage, fixed-bed gasifier with desulfurization of a first stream of fuel gas from the gasifier and the combustion of a second stream of fuel gas from the gasifier in a combustion device to treat sulfur sorbent regeneration gas resulting from the desulfurization of the first stream of fuel gas.
Fuel gas derived from the gasification of coal has been found to be useful as a combustible medium in many applications and processes. Of particular interest is the use of fuel gas in integrated gasification combined cycle systems which offer substantial advantages over many presently known power generating systems. Of the various types of gasifiers, such as entrained bed, fluidized bed, and fixed bed gasifiers, which can be used to provide fuel gas in such combined cycle systems, the fixed-bed gasifier appears to be a promising candidate. Fixed-bed gasifiers have many desirable features, but they also have several attendant shortcomings or drawbacks which detract from their usefulness in such combined cycle systems. For example, single-stage, fixed-bed gasifiers require the use of a sized coal feed in order to limit the quantity of fines that are discharged from the gasifier with the fuel gas. Also, fuel gases discharged from such fixed-bed gasifiers contain considerable amounts of tars, light oils, and ammonia which present environmental and equipment problems when used. Further, in order to meet environmental emission standards and to protect power generating devices, sulfur species, such as hydrogen sulfide and carbonyl sulfide, released from sulfur-containing coal during the gasification thereof must be essentially removed from the fuel gas prior to its utilization by employing a suitable desulfurization process such as one using a regenerable solid sulfur sorbent. In such instances, it is frequently desirable from the standpoint of sulfur-sorbent cost and availability to employ a sorbent which can be regenerated and recycled in the desulfurization process for reuse in sulfur removal operations. Regeneration of sulfur-containing sorbents may be achieved by contacting the sulfur-containing sorbent with a regenerating gas such as air so that the oxygen in the air can react with the captured sulfur species to convert them to sulfur oxides. During this regeneration, the converted sulfur species in the sorbent are released from the sorbent into the regeneration gas. This regeneration gas must then be treated to remove the sulfur oxides such as by converting them to environmentally acceptable forms of solid compounds which may be safely discharged into the environment. The satisfactory treatment of the regeneration gas containing the sulfur oxides is one of the principal problems associated with hot-gas desulfurization technology.